Understanding the anatomy of the MB root of the maxillary molar is crucial to endodontic treatment success. Surprisingly, Endodontists still often hear some clinicians say " I have a lot of success doing maxillary molar endo and while I do treat the occasional MB2, I don't believe the high percentages that are quoted in the research." Whether you choose to believe it or not, the fact remains that the literature does support the occurrence of MB2 in an extremely high number of first molars and many second molars. Ask your endodontist about the most common reason for retreatment of maxillary molars and you will find universal agreement that a missed MB2 is the first place that we look.
Here are a few studies that support this finding:
1. Incidence and configuration of canal systems in the mesiobuccal root of maxillary first and second molars. Kulild JC, Peters DD. J Endod 1990 Jul;16(7):311-7 The canal systems were type 1, 4.8%; type 2, 49.4%, and type 3, 45.8%. (Editor's note - almost 46% of cases of these were TOTALLY SEPARATE CANALS with TOTALLY SEPARATE FORAMINA ! )
2. An SEM investigation of the mesiolingual canal in human maxillary first and second molars. Gilles J, Reader A. Oral Surg Oral Med Oral Pathol 1990 Nov;70(5):638-43 The results demonstrated that 90% of first molars and 70% of second molars had two canals in the mesiobuccal root. Type 3 canal systems occurred in 33% of first molars and 35% of second molars. Eighty-one percent of first molars and 59% of second molars had a separate mesiolingual canal orifice.
3. Canal configuration in the mesiobuccal root of the maxillary first molar: a clinical study. Fogel HM, Peikoff MD, Christie WH. J Endod 1994 Mar;20(3):135-7 31.7% had two separate apical foramina (Weine Type III) and 82 39.4% had two canals that joined (Weine Type II). In 28.9% cases only one canal was located.
4. Canal morphology of maxillary molars: clinical observations of canal configurations. JJ Stropko J Endod 1999 Jun;25(6):446-50 The MB2 canal was found in 802 (73.2%) first molars, 310 (50.7%) second molars, and 5 (20.0%) third molars. It occurred as a separate canal in 54.9% of first molars, 45.6% of second molars, and joined in all third molars. However, as the operator became more experienced, scheduled sufficient clinical time, routinely employed the dental operating microscope, and used specific instruments adapted for microendodontics, MB2 canals were located in 93.0% of first molars and 60.4% in second molars.
5. Clinical investigation of second mesiobuccal canals in endodontically treated and retreated maxillary molars. Wolcott J, Ishley D, Kennedy W, Johnson S, Minnich S. J Endod 2002 Jun;28(6):477-9 The significant difference in the incidence of a MB2 canal between initial treatments and retreatments suggests that failure to find and treat existing MB2 canals will decrease the long-term prognosis.
6. Effect of magnification on locating the MB2 canal in maxillary molars. Buhrley LJ, Barrows MJ, BeGole EA, Wenckus CS. J Endod 2002 Apr;28(4):324-7 When the maxillary first molars were considered separately, the frequency of MB2 canal detection for the microscope, dental loupes, and no magnification groups was 71.1%, 62.5%, and 17.2%, respectively. The results of this study show that the use of magnification in combined groups leads to a MB2 detection rate approximately three times that of the nonmagnification group and that the use of no magnification results in the location of significantly fewer MB2 canals. Based on these results, more emphasis should be placed on the importance of using magnification for locating the MB2 canal.
The results of the literature clearly illustrate that MB2 canals occur in a high percentage of cases and that magnification is the key to finding them. At a minimum, strong loupes are required, but the best results obtained through the use of the Surgical Operating Microscope ( SOM). That is why they have become a standard part of the Endodontist's armamentarium.
Now that we acknowledge that they exist, what is the best method for finding them? The first thing we have to remember is to NOT go blindly burring into the MB area in the hope of locating the orifice. This has to be done methodically and with purpose. In this month's EndoFiles we will examine a few strategies for easier location and treatment of the elusive MB2.
TIP #1 - Use the right tools ! Dull DG 16 Explorers won't do !If you are going to do molar endo, you have to think of explorers as expendable instruments, just like files. One of the best tools is a JW (West) explorer. It is an ultra-thin version of a DG 16 that is very sharp and is useful in locating small orifices. But, it is easily bent and must be considered "disposable". You can't keep them forever. It is available through CK Dental instruments.
TIP #2 - Approach the MB2 canal from the Distal Angle. Most dentists attempt to explore for the orifice and locate MB2 by trying to place the tip of an endo explorer vertically into the pulpal floor groove that runs from the MB1 to the Palatal. This is an error. Here is why: the orifice of MB2 frequently has a dentin "lip" over it that covers the orifice the MB1<-> P groove. This lip arises from the mesial aspect. Therefore the actual orifice is often pointed at a 45 degree angle occlusally (toward the distal !) This initial exploration for the orifice is best accomplished by angling the instrument or handpiece so that it approaches MB2 directly from the distal aspect at an angle of about 45 degrees distal to the pulpal floor. When removing this dentin you need to use a small slow speed round bur or ultrasonic troughing instrument. (see diagram) The middle of the explorer or handpiece head will be either over the distal marginal ridge, rather than vertical in the access.